1. Field of the Invention
The present invention relates to environmental sealing of substrates such as cables or pipes, particularly within a duct. or a splice case. This may be done to prevent water, gas or other contaminant from passing along a duct into a manhole etc, or to protect a cable splice from the environment.
2. Description of the Related Art
The invention will be described primarily in terms of a duct seal, (which term includes "feedthroughs") but the invention is also applicable to other instances of sealing, including splice cases, pipe protection and grommets etc.
The reason that a seal (rather than an adhesive bond of no significant thickness) may be required is a disparity in size or shape between the substrate to be sealed and some other object such as a housing within which it lies. For example, a duct may be from several millimetres to several centimetres larger than the cable or other substrate that it carries, an oval cable may lie within a circular duct, or the installed size of a splice case housing may be larger than the spliced cables within it. Also, when a branch-out between two or more cables is to be sealed it will generally be necessary to convert their combined concave cross-section to a convex shape that can be enclosed by, say, a rigid wrap-around or other casing or by half-shells or a dimensionally-recoverable (generally heat-shrinkable) sleeve.
Such seals have usually been formed by the use of a conformable sealing member, for example an O-ring, or the use of a mass of sealant or a hot-melt adhesive. Whilst these seals in general work in a satisfactory manner, problems sometimes occur. For example, by their nature. conformable sealing members have a low modulus and especially where they are used to fill large voids, may have a tendency to creep over extended periods of time. Also, leak paths may occur if it has not been possible to introduce sufficient heat into a hot-melt adhesive to melt it. It is for example difficult to introduce heat into a duct.
Difficulties may also arise due to the materials needed for ducts and cables, which may be incompatible. Cables are often made of polyethylene or lead, and ducts of polyvinyl chloride, steel or cement which may be dirty or crumbly and difficult to clean.
A widely used duct seal, disclosed in Britsh patent number 1594937 assigned to the assignee of the present invention, comprises a hollow body member provided on its inner and/or outer surface with a plurality of spaced apart flanges, each flange extending away from and around said surface and at least a portion of the flange remote from said surface being deformable, but only at an elevated temperature, and at least part of said surface(s) and/or the surface of the flanges having a sealant thereon.
European patent application publication number 0179657 assigned to the assignee of the present invention discloses a duct seal especially for sealing about four cables which contains a spring which, when operated, radially-expands that part of the duct seal that is to seal to the duct. The cables are sealed by heat-shrink outlets of the duct seal. The spring is operated after heating the part of the duct seal in which it lies. Heating may soften the material of the seal and activate an adhesive.
European patent application publication number 0152696 assigned to the assignee of the present invention discloses an assembly for sealing an aperture (such as that between a duct and a cable it carries) which comprises a flexible envelope that is arranged to be wrapped on itself for insertion into the aperture, the envelope having an opening therein for receiving an expansible or expanding filler material. for example a curable foam, for expanding the envelope, a container containing said expansible filler material. and means arranged to connect the container to the envelope to conduct the filler thereto for effecting expansion of the envelope. characterized in that an adhesive or sealant is located on or associated with at least part of the outer surface of the envelope.
Other patent specifications disclosing hollow envelopes for sealing include the following. European patent application publication number 0100228 assigned to the assignee of the present invention discloses a method forming a seal between at least one elongate object and a surface surrounding the or each object. which comprises:
(a) positioning between the object and the surface a flexible envelope containing a void-filling composition which is capable of undergoing a change from a state of lower viscosity to a state of higher viscosity; PA1 (b) deforming at least part of the envelope thereby causing the void-filling composition to conform to the object and to the surface; and PA1 (c) causing said change from lower to higher viscosity. PA1 whereby cables may enter said casing through said aligned cutouts, and PA1 inflatable seal means confined between each of said pair of panels of said end walls and having openings aligned with said panel openings, said inflatable means being expandable, when so confined, against such cables passed through said end wall openings, characterized in that PA1 said end walls are removable from the said means to retain them, and PA1 said semi-circular disc portions are pivotally pinned to each other with their cut-outs presented together to form said openings of said panels PA1 whereby said semi-circular disc portions may be pivotally opened apart for placement about said conduits. PA1 a hole directly through a wall or between walls thereof through which hole a probe can be inserted (and from which it can preferably be removed by mere pulling) to introduce pressurizing medium into the member, and PA1 means by which the hole is automatically sealed on withdrawal of the probe.
European patent application publication number 0210807 assigned to the assignee of the present invention discloses a double-walled article, two of which may be used one around the other to form a duct seal, in the form of a tube having a small volume filling of a friction reducing liquid (preferable of high boiling point and low vapour pressure) or solid between its two walls. The article is able to revolve over a substrate by shear between its two walls to provide environmental or electrical protection.
Britsh patent number 2006890 discloses a seal comprising a container formed from resilient plastics sheet and partially filled with a liquid which is provided between a protective tube in a wall and insulation layer around a pipe. The container is of substantially toroidal shape and permits the pipe to move axially and radially whilst maintaining a seal between the insulation layer and the tube.
U.S. Pat. No. 3,038,732 discloses an inflatable seal bushing for sealing a pipeline casing, which comprises a hollow resilient means having an inflated configuration to match the inside surface of said casing and to contact the outside surface of the pipe of said pipeline. means for introducing a fluid into said hollow resilient means to inflate same, and a plurality of angularly disposed. relatively solid spacer means integral with said hollow resilient means and transverse thereto for centring and supporting said pipe within said casing, each of said spacer means having a passage therethrough for providing liquid communication in the hollow interior of said hollow resilient means.
U.S. Pat. No. 2,816,575 discloses an apparatus for laying a pipe employing inflated annular sealing rings.
U.S. Pat. No. 3,339,011 discloses a pneumatically-sealed cable splice case comprising a longitudinally-split sealable cylindrical casing having means within and adjacent to each of its longitudinal ends to retain and space apart a pair of end wall panels each end wall panel including two semi-circular disc portions having rounded outer edges and inner edges including aligned cut-outs therealong.
An inflatable packing device for insertion between mating surfaces of the hub and spigot ends of a pipe joint is disclosed in British patent number 1077314.
A hollow-walled sleeve into which fluid is to be injected for heat-insulation of ducts is disclosed in British patent number 1421960.
An inflatable closure member having a sealing material thereof, and used for sealing cables is disclosed in British patent number 2028601.
U.S. Pat. No. 9,07,136 discloses a packing for pipe joints formed by folding an open mesh fabric and applying a glue etc.
Whilst many of the articles disclosed in the above specifications are able to provide satisfactory seals, some problems remain. For example the use of curing or otherwise setting materials may prevent or make difficult subsequent removal of the article, and simple gas pressurization of a seal will generally mean that the article has a short life-time due to leaks or gas-diffusion. Also expensive,. cumbersome, easily-damaged and corrodable metal valves are required that protrude from the articles.